In regard to the development of cancer, the traditional belief is that genetics (family history) are the primary risk factor. Indeed, there do appear to be familial patterns of inheritance of some diseases including cancer. That familial pattern, however, doesn’t necessarily mean that genetics are the culprit.
When it comes to susceptibility to cancer, genetic predisposition does not tell the whole story. It’s often said that genetics ‘loads the gun’ and environment ‘pulls the trigger’. Ultimately, lifestyle factors are what sets the process into action.
For example,
it’s clear that smoking is associated with lung cancer. Granted, there are no randomized controlled trials on smoking, so we rely on epidemiological data, but the relative risk of smoking for lung cancer is so overwhelmingly high that there’s no question about causality.
BUT . . . there are some smokers who never develop lung cancer. It’s not fully understood, but this lucky bunch must have an amazing milieu of genetics that keeps them protected despite being bombarded by carcinogens. AND . . . unfortunately, there are some individuals who develop lung cancer despite never smoking, suggesting that they started with a predisposition to developing cancer and then some environmental factor ‘pulled the trigger’.
Genetics vs Environment
This gene theory of cancer originated in 1914 by Theodor Boveri, based primarily on his observations of chromosomal patterns in nematodes (i.e. parasitic roundworms) and sea urchins (ref). Subsequent research, however, demonstrated that cancerous nuclei (containing the genes) into normal cells did not negatively impact the cell and that transferring healthy cytoplasm into cancerous cells suppressed the cancer. Furthermore, more recent research confirmed that the mitochondrial component of the cytoplasm was the important factor in determining the status of the cell, as transferring cancerous mitochondria into a healthy cell induces cancer.
Studies of cancer among twins shows that genetics have a relatively small role in the development of cancer, whereas environment has significantly more effect (ref). It begs the question: why, then, do we observe familial patterns in some cancers?
Familial Inheritance
Familial patterns of inheritance are mostly driven by adopted patterns of lifestyle. Family members tend to learn the behaviors of their parents, and these behaviors tend to generate similar results in terms of their health. If you grew up in a household that prioritized sugary desserts after meals, it’s likely that you do the same.
We’ve been taught that obesity, diabetes, and cardiovascular disease are strongly linked to genetics. Instead, I believe that there are multiple reasons for familial patterns in metabolic disease: behavioral/cultural, epigenetics, inherited personal fat threshold (ref, ref), and a relatively small contribution from genes. Same goes for cancer – another metabolic disease.
